The present invention relates to loudspeaker enclosures of the low frequency exponential folded horn type. More specifically, it relates to front-loaded horn enclosures that are reflex ported and are intended for use in close proximity to at least one planar surface, such as a floor, ceiling or wall.
With the advent of the “Home Theatre” multi-channel market, there is a potential economic avenue for relatively large loudspeakers whose performance approaches the overall sound quality as might be found in commercial theatres. The use of horn loudspeaker enclosures provides the relative quality and the equivalent sound pressure levels that would also be associated with a commercial theatre experience while requiring a lower amount of wattage to achieve it. It is also sonically advantageous in multi-channel systems to use speaker types that are closely matched in efficiency and timbre. Horn loudspeakers capable of low frequency response are typically large in size, and are therefore less apt to be selected for domestic applications where the available floor space is a constraint.
The same issues of enclosure size and efficiency are also applicable to the public address and live music venues where portability and high sound pressure levels are desirable. A popular example of this type of loudspeaker enclosure can be seen in Klipsch, “La Scala”, Audio Engineering Society, Preprint No. 372, April, 1965. Whereas the cited example is not reflex ported, it features a bifurcated horn path of relatively simple design with a nominal low frequency cutoff (Fc) of approximately 70 Hz, and the overall size is of the enclosure is relatively compact.
The U.S. Pat. No. 4,138,594 to Klipsch teaches an exponential horn enclosure of relatively small dimensions also suitable for the applications described previously. The cited invention employs a folded exponential unitary horn path and is also not reflex ported. This example features a simple design and additionally presents a relatively small footprint for its performance capabilities, which is substantially similar to the previously cited example. It also features a nominal Fc of approximately 70 Hz.
The above cited prior art examples are known as front-loaded horns, in that the front of the driver feeds directly into the horn throat, and the back chamber for the driver is sealed from the atmosphere. The radiation of sound waves from the back of the driver cone is lost and therefore does not contribute to the overall sound pressure level being produced from the respective horn. The sealed back chamber is configured in volume to equalize the compliance of the back chamber with the reactance at the horn throat.
It is well known in exponential horn loudspeakers that the horn mouth cross-sectional area is determined by the wavelength of the lowest frequency to be produced. For horn loudspeaker enclosures that are intended to operate in proximity to planar surfaces, the cross-sectional area of the horn mouth can be made smaller in area and therefore, the overall dimensions of the horn enclosure can be reduced. It is also well known that the bifurcation of the respective horn at the throat provides for the smallest horn channel dimensions to be employed and for the folds to occur relatively close to the throat, which reduces the possibility of producing standing waves.
The formulas for calculating the values of exponential horns are well known in the art. Such examples can be found in the text “How to Build Speaker Enclosures”, by Alexis Badmaieff and Don Davis, Howard W. Sams and Company, Indianapolis, Ind., 13th printing (1978) pages 86 through 91. Additionally, information on reflex (also called phase inversion) porting can be found on pages 54 through 84.
The relative footprint of both of the above cited prior art examples is remarkably compact, however due to the relatively high low frequency cutoff of 70 Hz being employed, they are possibly best suited for vocal reproduction such as in public address use rather than being used in a full-range high fidelity role. It would therefore be advantageous to produce a new enclosure specifically combining an all-horn loaded loudspeaker of high efficiency, capable of a low frequency response suitable for high fidelity use, with a footprint size and overall appearance desirable for domestic applications in addition to public address use.